PDW V2.13
This is very similar to Winflex and works better because it can decode flex thorough the sound card. PDW is freeware!

Download here

This now works fully with windows XP.
Requires Windows 95/98/98se/2000/XP and the  interface  or a sound card for this to work.

WINFLEX V1.0
This is one of the  best programs we've found.
 Supposedly it was stolen from Motorola as rumor has it.

Requires Windows 95/98/98se and the  interface for this to work.

 THIS SOFTWARE WILL NOT WORK WITH WINDOWS XP!

Download here

POC32 V2.06
Works using your sound card.
It's a great shareware program, this requires no hardware to be built unless you want to decode more than two signals at once.
The down side is it doesn't decode all  the messages with the soundcard.
 Flex not supported.
Requires Windows 95/98/98se and the  interface  or a sound card for this to work.

Download here

Pocflex
Similar to Winflex this is the DOS Version
Requires DOS and the interface

   Download here

PD205
Works Ok. Good program to leave running
 forever on that old 386.
PD runs on an IBM PC or equivalent, anything from an 80286 upwards. It requires 512K of conventional memory and a small amount of hard disk PD runs from DOS, running from Windows is not recommended. interface Required for this to work

Download here

Pocsag/Flex decoder REV 0.004
DOS based very similar to PD204
Seems to work OK.
 
Download here